Add Strings

add_strings.rb

"""
  Adds two strings representing non-negative integers.

  Args:
    num1: A string representing a non-negative integer.
    num2: A string representing a non-negative integer.

  Returns:
    A string representing the sum of num1 and num2.
"""

def add_strings(num1, num2)
  i = num1.length - 1
  j = num2.length - 1
  carry = 0
  result = ''

  while i >= 0 || j >= 0
    n1 = i >= 0 ? num1[i].ord - '0'.ord : 0
    n2 = j >= 0 ? num2[j].ord - '0'.ord : 0

    sum = n1 + n2 + carry
    carry = sum / 10
    result = (sum % 10).to_s + result

    i -= 1
    j -= 1
  end

  if carry > 0
    result = carry.to_s + result
  end

  result    
end